Five stars are useful information. They become less useful when you treat them as a universal score that makes every five-star vehicle equally safe in every situation.
NHTSA's program reports crash-test and rollover performance, with five stars at the top of its scale. Open the rating for the exact model year and applicable configuration and look at the individual results. The overall score is a starting point.
Compare vehicles the way the tests allow
For frontal ratings and the Overall Vehicle Score, NHTSA limits comparisons to vehicles in the same class and within 250 pounds of one another. Side-crash and rollover ratings can be compared more broadly.
That distinction matters when a shopping list includes a small car and a much larger SUV. Matching stars do not establish identical real-world protection. Before drawing a conclusion, check whether the ratings are intended to answer the comparison you are making.
Also read any safety-concern symbol on the results. NHTSA explains that a concern can appear even when a vehicle has a high overall rating; those concerns are not part of the overall-score calculation. The notes can therefore change what you take from the headline.
An unrated category is not a failed test
A category marked not rated means it has not been rated under that part of the program. It does not supply a score you can safely assume in either direction.
For a used car, ratings also leave the condition of the actual vehicle to be evaluated. The original testing cannot tell you whether its tires are worn, a warning light has been ignored, or damage was properly repaired. Equipment listed for a model needs to be present and working on the car you select.
Use the ratings to improve a comparison, then connect them with the vehicle's equipment, current recall information, and inspection. A safety decision deserves more attention than sorting a list by the biggest number of stars.